It doesn't matter. Not even going to delve into your ethic complaints because it has been shown that monsters that die turn into smoke and explained by the dragon that lower level monsters do not "think", they have instincts that amount to "kill humans". You can make assumptions but you won't have anything to back up what you say.
Like, even assuming I accept this premise (...assumptions that you have made up, with similarly little to back it up, or so I feel. Or at least I interpreted the setting at least somewhat differently) he didn't seem particularly concerned about enslaving the dragon either, no? I'm not sure where you're going with this.
Also this statement that they're normally unthinking monsters who unilaterally attack humans totally would support my original statement (That it's obvious someone killing one could have no idea they were doing anything wrong, and that judging them for that, much less killing them for it, is quite unfair).
The society was the HIDDEN elf village. These intruders decided to come to their village and without a care in the world ended up, as far as we know, killing chappi. You can't go "Oh, it's a misunderstanding that I killed your friend."
Right, I said from the get-go his murderous reaction was
understandable.
Though I can't agree with your implication about the "hidden"-ness of the village proving their ill-intent. That's an absurd leap. No reason to think their motives were different from what they said—if there'd been even a
smidge more interaction first and the protagonist had gotten to see that they were Totally Bad Dudes™, there wouldn't be an issue. But that's not what happened.
These sort of these lead to blood feuds/debts and even in our society if someone kills your friend and you're due to a misunderstanding you're legally allowed to neutralize the target that killed your friend. It is your responsibility to make informed decisions - and in this case they didn't bother so they're getting their retribution.
I... So, to be fair, I don't know what country you live in. But in every modern country I am aware of, vigilante killings are quite strictly illegal. Most states in the U.S., whose laws I am most familiar with, it would, at best, be good evidence in use for arguing for second-degree murder instead of first-degree.
If you're talking about something like a citizen's arrest, this isn't that.
I mean, in a world of gods and what not a God of Justice would've definitely counted this action as a sin against an innocent, misunderstanding be damned.
Depends on the setting, really. But I wasn't talking about some god's opinion, I was talking about mine.
Now: If you'd wanted to argue the relative moral values of medieval societies vs. modern ones—which I think is what you're getting at here?—that's a totally reasonable way to look at it, sure. But I myself am not really inclined to do so here. Series that take their grim medieval values seriously and sincerely (
The Emperor and the Female Knight comes to mind of the things I'm reading right now, but I digress) I will totally accept moral relativity from. Intricate made-up morality systems too, for that matter, if an author portrays them convincingly; actually those are quite interesting. But these guys... are totally modern-thinking blokes in a lazy medieval-lite fantasy setting, 98% of the time. The protagonist especially is clearly supposed to be "a relatable normal [modern] guy" in that respect at least. Accordingly I'm inclined to judge by modern values.
Edit: That said. If we
were going by medieval judgements the default answer here seems quite straightforward: "This Man is a Witch, allied with Evil Monsters, and hath Slain the Defenders of the Kingdom and bound their Souls to Undeath! Burn him."
Which is where the plot seems to be going, honestly, which is fair enough. But that's sort of besides either your or my points as to the
actual ethicality of the protagonist's actions. (By
our value systems).
I mention this only because of you bringing up my earlier point about the predictability of justice being a prerequisite of a relatively happy society: In medieval societies as we portray them today, justice is
quite predictable and very black-and-white. Incidentally, it would not in the protagonist's favor. But predictably so—and in fact strictly caused by his aversion to do what society wants of him (which in and of itself is fine; my point was that people need to be reasonably
able to judge the outcomes of their actions as relates to justice (and retaliation). But certainly not that everyone has to then stay out of trouble).